Plants which are substantially “tolerant” to a herbicide when they are subjected to it provide a dose/response curve which is shifted to the right when compared with that provided by similarly subjected non tolerant like plants. Such dose/response curves have “dose” plotted on the x-axis and “percentage kill”, “herbicidal effect” etc. plotted on the y-axis. Tolerant plants will typically require at least twice as much herbicide as non tolerant like plants in order to produce a given herbicidal effect. Plants which are substantially “resistant” to the herbicide exhibit few, if any, necrotic, lytic, chlorotic or other lesions when subjected to the herbicide at concentrations and rates which are typically employed by the agricultural community to kill weeds in the field in which crops are to be grown for commercial purposes.
It is particularly preferred that the plants are substantially resistant or substantially tolerant to herbicides (hereinafter “glyphosate”) which have 5-enol pyruvyl shikimate phosphate synthetase (hereinafter “EPSPS”) as their site of action, of which N-phosphonomethylglycine (and its various salts) is the pre-eminent example.
The herbicide may be applied either pre- or post emergence in accordance with usual techniques for herbicide application to fields comprising crops which have been rendered resistant to the herbicide. The present invention provides, inter alia, nucleotide sequences useful in the production of such herbicide tolerant or resistant plants.